U.S. patent number 10,872,437 [Application Number 16/267,110] was granted by the patent office on 2020-12-22 for face authentication method.
This patent grant is currently assigned to IDEMIA IDENTITY & SECURITY FRANCE. The grantee listed for this patent is IDEMIA IDENTITY & SECURITY FRANCE. Invention is credited to Jean Beaudet, Julien Doublet.
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United States Patent |
10,872,437 |
Doublet , et al. |
December 22, 2020 |
Face authentication method
Abstract
The invention relates to a method for authenticating a face
presented to a device comprising the steps in which the imager
acquires an initial image of a face, the processing unit determines
a pose of the face from the initial image, and determines a
reference pose and a target position placed randomly or
pseudo-randomly in a target space, the screen displays a displayed
image (6) comprising at least one visual orientation mark (7)
initially at a reference position, and a visual target (8) at the
target position, updated by moving the visual orientation mark (7)
according to the successive poses of the face, and the processing
unit authenticates the face presented if there is a match between
the position of the visual orientation mark (7) and the target
position where the visual target is located (8).
Inventors: |
Doublet; Julien (Courbevoie,
FR), Beaudet; Jean (Courbevoie, FR) |
Applicant: |
Name |
City |
State |
Country |
Type |
IDEMIA IDENTITY & SECURITY FRANCE |
Courbevoie |
N/A |
FR |
|
|
Assignee: |
IDEMIA IDENTITY & SECURITY
FRANCE (Courbevoie, FR)
|
Family
ID: |
1000005257929 |
Appl.
No.: |
16/267,110 |
Filed: |
February 4, 2019 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20190244390 A1 |
Aug 8, 2019 |
|
Foreign Application Priority Data
|
|
|
|
|
Feb 6, 2018 [FR] |
|
|
18 50967 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06T
7/74 (20170101); G06F 21/32 (20130101); G06K
9/00288 (20130101); G06T 2207/30201 (20130101) |
Current International
Class: |
G06T
7/73 (20170101); G06F 21/32 (20130101); G06K
9/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Fabio Remondino, 3-D reconstruction of static human body shape from
image sequence, Computer Vision and Image Understanding, (Year:
2003). cited by examiner .
Xie, Pengqing, "Facial movement based human user authentication",
Graduate Thesis and Dissertations, Iowa State University, 2014, pp.
1-51. cited by applicant .
Preliminary Research Report received for French Application No.
1850967, dated Aug. 10, 2018, 3 pages (1 page of French Translation
Cover Sheet and 2 pages of original document). cited by applicant
.
Patacchiola et al., "Head Pose Estimation in the Wild using
Convolutional Neural Networks and Adaptive Gradient Methods",
Pattern Recognition, vol. 71, Nov. 2017, pp. 132-143. cited by
applicant .
Galbally et al., "Biometric Antispoofing Methods: A Survey in Face
Recognition", IEEE Access, vol. 2, 2014, pp. 1530-1552. cited by
applicant .
European Search Report received for EP Patent Application No.
19155210, dated Apr. 8, 2019, 2 pages of Original Document Only.
cited by applicant.
|
Primary Examiner: Rachedine; Mohammed
Attorney, Agent or Firm: Womble Bond Dickinson (US) LLP
Claims
The invention claimed is:
1. A method for fraud detection during an authentication of a face
presented to a device comprising an imager, a screen and a
processing unit, comprising the steps in which: the imager acquires
at least one initial image of a face presented in the acquisition
field of the imager, the processing unit determines a pose of the
face from the initial image, and from this face pose, determines a
reference pose, a face pose being defined by at least two pose
angles representative of an orientation of the face appearing in an
image, and the processing unit determines a target position placed
randomly or pseudo-randomly in a target space at a distance from a
reference position corresponding to the reference pose, said target
position corresponding to a target pose of the face, the screen
displays a displayed image comprising at least one visual
orientation mark initially at the reference position determined
from the pose of the face in the initial image, and a visual target
at the target position, the imager acquires a stream of images of
the face presented in the acquisition field, and for each image of
a plurality of successive images of said image stream: the
processing unit determines a new pose of the face in said each
image of the plurality of successive images of said image stream,
and determines a new position of the visual orientation mark in
image corresponding to the new pose of the face with respect to the
reference pose in said each image of the plurality of successive
images of said image stream, the displayed image displayed by the
screen is updated by moving the visual orientation mark in the
displayed image to the new position of the visual orientation mark
in the displayed image corresponding to the new pose of the face
with respect to the reference pose in said each image of the
plurality of successive images of said image stream, the processing
unit authenticates the presented face when, following the
successive displacement of the visual orientation mark on the
successive new positions of said visual orientation mark in the
successively updated displayed image, there is a match between a
new position of the visual orientation mark successively moved in
the updated displayed image and the target position where the
visual target is located in the updated displayed image,
corresponding to a match between the face pose and the target pose,
otherwise the face presented in the acquisition field is considered
as fraud.
2. The method according to claim 1, wherein the target space
extends on either side of the reference position.
3. The method according to claim 1, wherein the target space
corresponds to angular ranges of the pose angles defining a
plurality of possible target positions.
4. The method according to claim 3, wherein the angles
representative of the orientation of the face appearing in the
image comprise a yaw angle about a vertical axis and a pitch angle
about a horizontal axis, the angular ranges extending between
.+-.10.degree. and .+-.20.degree. with respect to the pose angles
of the reference pose.
5. The method according to claim 1, wherein the processing unit
defines the target space also according to user data and/or
elements contained in the initial image.
6. The method according to claim 1, wherein a time is allotted at
the expiry of which, in the absence of match between the new
position of the visual orientation mark and the target position
where the visual target is located, the face presented in the
acquisition field is considered as fraud.
7. The method according to claim 1, wherein the match between the
new position of the visual orientation mark successively moved in
the updated displayed image and the target position where the
visual target is located in the updated displayed image, needs to
be maintained for a predetermined duration before the processing
unit authenticates the face.
8. The method according to claim 1, wherein, when the processing
unit determines a reference pose, the processing unit transmits an
order of movement of the face if the face pose does not correspond
to a front view of the face.
9. The method according to claim 1, wherein the authentication of
the presented face is also conditioned by the determination of the
three-dimensional appearance of the presented face by implementing
a photogrammetric reconstruction technique based on a movement from
at least two face images of the image stream corresponding to two
different poses.
10. The method according to claim 1, wherein the processing unit
determines, for the plurality of successive images of the image
stream, a direction of the face gaze by identifying an orientation
of the eyes of said face on said images of said images of said
successive images of the image stream, the authentication of the
presented face is also conditioned on a gaze in a direction of the
visual orientation mark and/or the visual target.
11. A computer-readable non-transitory medium comprising program
code instructions stored thereon for performing the steps of a
method according to claim 1 when said program is executed on a
computer reading said non-transitory medium.
12. A device comprising an imager, a screen and a processing unit,
said device being configured to implement a method according to
claim 1.
Description
TECHNOLOGICAL CONTEXT AND BACKGROUND
The present invention belongs to the field of biometrics, and
relates more specifically to a method for authenticating a
face.
Some identification or identity verification methods need to
acquire an image of the face of the person wishing to claim an
identity. It may be, for example, biometric identification methods,
based on the analysis of elements of the face to carry out an
identification. It may also be the comparison of the person's face
with photographs identifying said person, in particular when
submitting identity documents such as a passport. Finally, access
control methods based on facial recognition have recently emerged,
in particular to unlock a smart mobile phone, as in U.S. Pat. No.
9,477,829.
However, the implementation of these methods requires to be guarded
against fraud consisting in presenting, to the imager acquiring the
image of the face, a reproduction of the face, such as a
photograph. To this end, methods for authenticating the face, that
is to say detecting possible fraud, have been developed. Most of
these methods rely on the analysis of an imposed movement,
generally called challenge. Thus, the person whose face is
presented to the imager is for example asked to perform specific
actions such as blinking, smiling or nodding. However, such methods
have proved to be vulnerable to fraud based on video presentation,
videos in which a face performs the requested challenge.
Patent application US 2017/0124385 A1 describes a user
authentication method based on a challenge, i.e. the user must
perform an imposed sequence of movements. More specifically, the
system asks the user to stand first in a rest position facing the
camera, where it acquires a first feature of the face, then it asks
him to turn in order to acquire a second feature of the face.
Authentication is done by comparing the features in order to detect
an inconsistency representative of a fraud. The fraud-resistance
having such an approach is however not perfect.
PRESENTATION OF THE INVENTION
The aim of the invention is to overcome at least partially these
drawbacks and preferably all of them, and aims in particular to
propose a method for authenticating a face presented to a device
allowing to detect fraud, which is at the same time simple, robust
and effective against video presentation.
To this end, there is provided a method for authenticating a face
presented to a device comprising an imager, a screen and a
processing unit, comprising the steps in which: the imager acquires
at least one initial image of a face presented in its acquisition
field, the processing unit determines a pose of the face from the
initial image, and from this face pose, determines a reference
pose, a face pose being defined by at least two angles
representative of the orientation of the face appearing in an
image, and a target position placed randomly or pseudo-randomly in
a target space at a distance from a reference position
corresponding to the reference pose, said target position
corresponding to a target pose, the screen displays a displayed
image comprising at least one visual orientation mark initially at
the reference position determined from the pose of the face in the
initial image, and a visual target at the target position, the
imager acquires a stream of images of the face presented in its
acquisition field, and for a plurality of successive images of said
image stream: the processing unit determines a pose of the face in
each image of the plurality of successive images, the processing
unit determines successive positions of the visual orientation mark
according to the successive poses of the face with respect to the
reference pose in the plurality of successive images, the image
displayed by the screen is updated by moving the visual orientation
mark according to its successive positions determined according to
the successive poses of the face with respect to the reference pose
in the plurality of successive images, the processing unit
authenticates the presented face when, following the displacement
of the visual orientation mark, there is a match between the
position of the visual orientation mark and the target position
where the visual target is located, corresponding to a match
between the face pose and the target pose, otherwise the face
presented in the acquisition field is considered as fraud.
The method is advantageously completed by the following
characteristics, taken alone or in any of the technically possible
combinations thereof: the target space extends on either side of
the reference position; the target space corresponds to angular
ranges of the pose angles defining a plurality of possible target
positions; the angles representative of the orientation of the face
appearing in the image comprise a yaw angle about a vertical axis
and a pitch angle about a horizontal axis, the angular ranges
extending between .+-.10.degree. and .+-.20.degree. with respect to
the angles of the reference pose; the processing unit defines the
target space also according to user data and/or elements contained
in the initial image; a time is allotted at the expiry of which, in
the absence of match between the position of the visual orientation
mark and the target position where the visual target is located,
the face presented in the acquisition field, is considered as
fraud; the match between the position of the visual orientation
mark and the target position where the visual target is located,
needs to be maintained for a predetermined duration before the
processing unit authenticates the face; when the processing unit
determines a reference pose, the processing unit transmits an order
of movement of the face if the face pose does not correspond to a
front view of the face; the authentication of the presented face is
also conditioned by the determination of the three-dimensional
appearance of the presented face by implementing a photogrammetric
reconstruction technique based on the movement from at least two
face images of the image stream corresponding to two different
poses; the processing unit determines, for the plurality of
successive images of the image stream, a direction of the face gaze
by identifying the orientation of the eyes of said face on the
acquired images, the authentication of the presented face is also
conditioned on a gaze in the direction of the visual orientation
mark and/or the visual target.
The invention also relates to a computer program product comprising
program code instructions recorded on a non-transitory medium
usable in a computer for performing the steps of a method according
to the invention when said program is executed on a computer using
said non-transitory medium.
The invention finally relates to a device comprising an imager, a
screen and a processing unit, said device being configured to
implement a method according to the invention.
PRESENTATION OF THE FIGURES
The invention will be better understood thanks to the following
description which refers to embodiments and variants according to
the present invention, given by way of non-limiting examples and
explained with reference to the appended schematic drawings, in
which:
FIG. 1 shows a block diagram of steps implemented in the
authentication method,
FIG. 2 schematically shows a person presenting his face to a device
during the implementation of the method,
FIG. 3 schematically shows the angles defining the pose of a
face,
FIGS. 4a and 4b show schematic examples of images displayed during
a successful authentication, the presented face being considered as
an authentic face,
FIGS. 5a and 5b show schematic examples of images displayed during
a failed authentication, the presented face being considered as
fraud.
DETAILED DESCRIPTION
With reference to FIG. 2, the authentication method is implemented
by means of a device 1 to which a face 2 of a user is presented.
The device 1 comprises a processing unit, an imager 3 adapted to
acquire images of objects presented in its acquisition field 4, and
a screen 5 capable of displaying images to the user. More
specifically, the device 1 is configured so that the user can
simultaneously present his face 2 in the acquisition field 4 of the
imager 3, and look at the screen 5. The device 1 can thus be for
example a smartphone-type handheld device, which has typically a
suitable configuration between the imager 3 and the screen 5. The
device 1 can nevertheless be any type of computerized device, and
can particularly be a fixed terminal dedicated to the identity
checks, for example installed in an airport. The processing unit
comprises at least one processor and a memory, and allows executing
a computer program for the implementation of the method.
The user presents his face 2 in the acquisition field 4 of the
imager 3. The imager 3 acquires at least one initial image of the
face 2 (step S01). From the image of the face, the processing unit
determines a pose of the face, that is to say its orientation. As
illustrated in FIG. 3, the orientation of the face can be described
by three angles reflecting rotations about axes defined by the
common configuration of the faces. Indeed, a face includes a bottom
(towards the neck), a top (the forehead/the hair), a face where the
mouth and the eyes are fully visible, and two sides where the ears
are located. The different elements composing a face are
distributed according to obvious geometrical criteria in a front
view: the mouth is below the nose, the eyes are on the same
horizontal line, the ears are also on the same horizontal line, the
eyebrows are above the eyes, etc.
It is therefore easy to define for the face, from its image, an
orientation with respect to the device 1 based on the rotation of
the face about a vertical axis and at least one horizontal axis.
FIG. 3 shows a typical example of locating the orientation of a
face according to three angles about three orthogonal axes: a yaw
angle about a vertical axis 20, a pitch angle about a first
horizontal axis 21, and a roll angle about a second horizontal axis
22 roll angle The rotation about the vertical axis 20 corresponds
to the rotation of the head from left to right. The first
horizontal axis 21 corresponds to a horizontal axis about which the
head turns during a nodding. The second horizontal axis 22
corresponds to a horizontal axis comprised in a plane of symmetry
of the face, cutting the nose and the mouth and separating the
eyes. The rotation about this second horizontal axis 22 corresponds
to a head tilt to the left or to the right.
If the three angles can be used to define the pose, the roll angle
may, however, not be used because of the low amplitude of rotation
of a face in that direction and of the discomfort that can be
provided by this rotation. The pose can therefore be defined by at
least two angles representative of the orientation of the face
appearing in the image, which are preferably the yaw angle and the
pitch angle.
There are many known methods allowing to estimate the pose of a
face from one or more image(s) of that face. It is possible for
example to use a pose estimation method based on a deep learning
implemented by means of a convolutional neural network. The article
"Head Pose Estimation in the Wild using Convolutional Neural
Networks and Adaptive Gradient Methods" by M. Patacchiola and A.
Cangelosi, Pattern Recognition vol. 71, November 2017, pages
132-143, presents an example of a method that can be implemented to
determine the pose of the face.
Once the pose of the face is determined from the image of the face,
the processing unit determines a reference pose (step S02). This
reference pose will be subsequently used as a reference for face
poses. This reference pose may correspond directly to the pose of
the face. Preferably, however, the reference pose must meet certain
characteristics, and particularly present the face sufficiently
frontally to allow a good application of the authentication method,
and possibly of the identification method. Thus, when the
processing unit determines a reference pose, the processing unit
transmits an order of movement of the face if the pose of the face
does not correspond to a front view of the face. It is considered
here that the front view implies yaw and pitch angles less than
5.degree. with respect to an exact alignment of the second
horizontal axis 22 (i.e., the axis of the nose), with the viewing
direction. The order of movement is communicated to the user by any
means, such as for example by the display on the screen 5 of an
instruction text asking the user to stand in front of the imager 3,
or by an audio message.
To this reference pose corresponds a reference position, which will
be subsequently used as a position reference. For the sake of
simplicity, it is possible to define the reference position as
being a central position. Indeed, the reference position is
preferably predetermined and immutable. However, it is possible to
plan defining the reference position according to the content of
the acquired initial image, for example to match it with an element
of the face. The processing unit also determines a target
position.
The screen 5 displays a displayed image comprising at least one
visual orientation mark initially at the reference position, and a
visual target at the target position (step S03). FIG. 4a shows an
example of such a displayed image 6. Thus, as illustrated, the
displayed image 6 preferably includes the representation of the
face previously acquired by the imager 3. There is a visual
orientation mark 7 represented here by a black circle. Other
shapes, patterns or colors can be considered. For example, if it is
desired to use the roll angle, it is preferable to use then a
visual orientation mark 7 having an asymmetry by any rotation, for
example a visual reference mark 7 having a pattern such as a cross
or a square shape, so that the roll change of the face 2 can be
reflected by a rotation of the visual orientation mark 7 which is
visually perceptible. In the illustrated case, the reference
position where the visual orientation mark 7 is initially located
is in the center of the image.
There is also the visual target 8, here represented by three
concentric circles, placed at a target position. The target
position, and thus this visual target 8, is placed randomly or
pseudo-randomly in a target space at a distance from the reference
position. FIG. 4a shows an example of a target space 9, represented
by two dotted concentric ovals centered on the reference position.
Many other target spaces are possible. It should be noted that the
target space does not appear in the displayed image 6 that the
screen 5 displays, and that this representation is given only for
illustration purposes. The target space 9 represents the set of
possible target positions.
This target space 9 corresponds to angular ranges of the pose
angles defining a plurality of possible target positions. There is
indeed equivalence between the pose angles and the positions in the
displayed image 6. This equivalence can be interpreted as a frame
change. Thus, by noting that X and Y are the coordinates of a
position in the displayed image, X and Y can be expressed as a
function of the yaw and pitch angles, considering the reference
position at the center of the image and the reference pose as
having zero yaw and pitch angles:
.times..times..times..times..times..times..times..times..times..times..t-
imes..times..times..times..times..times..times. ##EQU00001##
wherein k.sub.1 and k.sub.2 are amplification factors that can be
equal, and the angles are in degrees. This is a non-limiting
example, other formulae can be used, for example with angles in
radians, different maximum angles (here of .+-.90.degree.), or a
non-centered reference position. It is even possible to use
nonlinear formulae.
There is a bijection between a position on the displayed image and
a pose of the face. Thus, the target position corresponds to a
target pose. It is also possible that the processing unit
determines a target pose in a target space 9 (this time angular
space), and deduces a target position therefrom. The user will have
to change the pose of his face 2 so that it corresponds to the
target pose. Due to the link between a position in the image and a
pose of the face, it is preferable to restrict the possible target
positions to target poses that can be comfortably performed by a
user, that is to say to restrict the angular ranges to which the
target space 9 corresponds. In addition, it is preferable to
restrict the possible target positions to target poses requiring a
sufficiently significant pose change, that is to say a target
position at a distance from the reference position. Consequently,
the angular ranges defining the target space 9 preferably extend
between .+-.10.degree. and .+-.20.degree. with respect to the
angles of the reference pose, at least for both used angles (yaw
angle and pitch angle). Preferably, the target space 9 extends on
either side of the reference position, for example on the right and
on the left, and not on only one side.
It is possible that the processing unit defines the target space 9
also according to user data and/or elements contained in the image,
for example by restricting the target space 9. It is possible for
example to change the location or the extent of the target space 9
according to the disposition of the face in the initial image. It
is also possible to adapt the target space 9 in order to take into
account physical characteristics of the user, such as his height,
his age or a possible handicap. Since the target space 9 is
preferably defined with respect to the reference position, it is
possible to change the target space 9 by moving the reference
position, which can also be placed according to user data and/or
elements contained in the image.
The target space 9 has continuity at least piece-wise, that is to
say it covers one or more extent(s) on the displayed image 6. There
is therefore a large number of possible target positions, at least
more than 100, even more than 1000. In fact, the continuity of the
target space 9 covers a quasi-infinite number of possible target
positions. Since the target position is placed randomly or
pseudo-randomly in the target space 9, the target position changes
each time the method is implemented. It is therefore not possible
for a fraudster to predict in advance where the target position
will be, nor to predict all possible target positions. As a result,
it is inoperative to present to the imager 3 a video representing a
face taking target poses based on previous implementations of the
method, since the target position varies between each iteration of
the method.
After the displayed image 6 has appeared on the screen 5, the user
must match the position of the visual orientation mark 7 with the
target position, by moving the visual orientation mark 7 to the
visual target 8. To do so, the user changes the pose of his face,
which change is reflected by the displacement of the visual
orientation mark 7. The imager 3 then acquires a stream of images
of the face 2 presented in its acquisition field 4, and the
processing unit analyzes a plurality of successive images of said
image stream in order to update the displayed image 6 to inform on
the displacement of the visual orientation mark 7 reflecting the
changes in the pose of the face 2.
Thus, for each of the successive images, the processing unit
determines the pose of the face appearing in the image (step S04).
The pose of the face is determined in relation to the reference
pose. From the pose of the face, the processing unit determines an
updated position of the visual orientation mark 7 in the displayed
image 6 (step S05). The image displayed 6 by the screen 3 is
updated by moving the visual orientation mark according to its
updated position (step S06). As illustrated, it is preferable to
also display each acquired successive image, so that the user can
see his face on the screen 5. The image stream corresponds, in
fact, to a video and the reiteration of the procedure follows the
frame rate of the video.
This procedure is repeated as long as authentication or fraud
detection conditions are not met. At each image or at certain time
intervals, the processing unit checks whether authentication or
fraud detection conditions are met. Particularly, the processing
unit checks whether there is match between the position of the
visual orientation mark and the target position (step S07), which
corresponds to a match between the face pose and the target pose.
It is well understood that the match must be dealt with a tolerance
interval around the target position, it would not be reasonable to
require a pixel-precise tolerance. Preferably, the visual target 8
has a certain surface, and it is considered that there is match
when the visual orientation mark 7, or at least part of it, covers
at least part of the surface of the visual target 8.
Preferably, it is required that the entire visual orientation mark
7 covers at least part of the surface of the visual target 8. This
is the case illustrated in FIG. 4b.
When there is match between the position of the visual orientation
mark and the target position, the processing unit authenticates the
presented face 2 as corresponding to an authentic face, that is to
say not being a fraud. However, if this match is a necessary
condition, it is preferably not sufficient. It is preferable to add
stability and time criteria conditioning authentication of the
face. As an example of a stability criterion, it can be provided
that the match between the position of the visual orientation mark
and the target position needs to be maintained for a predetermined
duration before the processing unit authenticates the presented
face 2. Such a predetermined duration can be for example greater
than 0.5 seconds, and preferably greater than 1 second, or even 1.5
or 2 seconds. Thus, a fraud based on the presentation of a video
where a face would quickly perform different poses in the hope that
one of them corresponds to the target pose, would not be effective,
since holding each pose for the predetermined duration would be too
long. Moreover, there is thus protection against an accidental
match that would occur transiently during a movement of the face
presented when the target position would be in the path of the
visual reference mark 7.
Face authentication can also be conditioned by determining the
three-dimensional appearance of the presented face 2 by
implementing a movement-based photogrammetric reconstruction
technique from at least two images of the face of the image stream
corresponding to two different poses. It is in particular possible
to implement a Simultaneous Localization and Mapping (SLAM)
technique. Other conditions may result from the implementation of
different fraud detection methods, in particular to detect
fraudulent artifacts such as Moire detection, representative of the
artificial appearance of the presented face 2.
The direction of the gaze can also allow improving the face
authentication modalities. Typically, if the gaze is not directed
toward the visual orientation mark 7 or the visual target 8, the
face may be considered as fraudulent. Indeed, in order to move the
visual orientation mark 7, it is necessary for the user, on the one
hand, to locate the visual target 8 at the target position, and
therefore look at it, at least at the beginning and, on the other
hand, to control the displacement of the visual orientation mark 7
by looking at it. Thus, if the user's face gaze should be oriented
in a direction other than either of these positions (which should
normally tend to get closer), such a singularity would be a strong
indication that the face is not authentic.
Therefore, the processing unit preferably determines, for the
plurality of successive images of the image stream, a direction of
the face gaze by identifying the orientation of the eyes of said
face, and the authentication of the presented face 2 is then also
conditioned on a gaze of the face in the direction of the visual
orientation mark and/or of the visual target. If the gaze of the
face is in a direction too far from the visual orientation mark
and/or from the visual target, the presented face 2 is not
authenticated. It is even possible to take into account the
correlation between the displacement of the direction of the face
gaze and the successive positions of the visual orientation mark to
estimate if the tracking of the displacement of the visual
orientation mark by the gaze corresponds to an authentic face.
Moreover, a time is allotted at the expiry of which, in the absence
of match between the position of the visual reference mark 7 and
the target position, the face 2 presented in the acquisition field
4 is considered as fraud. For example, this allotted time may be
less than 10 seconds, or even less than 5 seconds, counted between
the appearance of the visual target 8 and the end of the method.
This allotted time allows to temporally restrict the execution of
the method, and allows in particular to avoid a fraud based on the
presentation of a video where a face would perform different poses
in the hope that one of them corresponds to the target pose,
because of the time required to do so, especially if the
maintenance of the target pose for a predetermined time is
required.
Thus, if the authentication conditions, including a match between
the position of the visual orientation mark and the target
position, are met, the processing unit authenticates the presented
face 2 (step S08). The authentication of the presented face 2 can
then be used to continue identification conducted in parallel.
Conversely, if at the end of an allotted time, the authentication
conditions have not been met, the face is considered as fraud.
Thus, in the example of FIGS. 5a and 5b, the visual target 8 is
disposed at the top right of the displayed image 6. The reference
position, where the visual orientation mark 7 is initially
positioned, is central, as FIG. 4a. In response to the display of
the displayed image 6 by the screen 5, the presented face 2
performs a pose change which brings the visual orientation mark 7
on the left of the displayed image 6. It is the location which was
that of the visual target 8 in the example of FIGS. 4a and 4b. It
is therefore probably a fraud based on the presentation of a video
replaying a previous response to the challenge proposed by the
method. Nevertheless, since the positioning of the visual target 8
changes with each implementation of the method, and since there is
a quasi-infinite number of possible target positions, knowledge of
a previous implementation of the method does not allow the
fraudster to authenticate the presented face 2. In this case, since
the visual orientation mark 7 clearly does not clearly match with
the visual target 8, when the allotted time has elapsed, the
challenge is considered as failed and the face 2 presented in the
field acquisition 4 is considered as fraud.
In such a case, a fraud alert can be set up, for example by
preventing identification conducted in parallel, and/or alerting
security personnel. It is also possible to provide an information
to the user informing him of the failure of authentication of the
presented face. As it is a first failure, it is possible to
re-implement the method in order to give the user a second
chance.
The invention is not limited to the embodiment described and shown
in the appended figures. Modifications remain possible, especially
from the point of view of the constitution of the various technical
characteristics or by substitution of technical equivalents,
without departing from the field of protection of the
invention.
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